docs: def missing_requirements_command(missing_programs, installation_string,
                                   filename, unused_lines):
      """Pseudo-command to be used when requirements are missing."""
      verb = 'is'
      if len(missing_programs) > 1:
          verb = 'are'
      return {
          filename: {
              'skipped': [
                  '%s %s not installed. %s' % (', '.join(missing_programs), verb,
                                               installation_string)
              ]
          }
      }